Knives are gray areas in some states. If it can be considered a tool, you probably won't get locked up. You say the knife is in a hiking bag in your trunk. I doubt that will present an issue. I had a guy I pulled over the other day that had a twelve inch machete under his front seat. He said he used it for lawn work. I removed it from the sheath and it was covered in grass. In the area I work in, I would have a hard time charging him. On the other hand, a fellow officer charged a young'in with concealed deadly weapon for having a fixed blade knife unsheathed and taped to the underside of his front seat. He also found a couple crack rocks. Long story short, it's all about the circumstances and purpose. If you have a fixed blade in a hiking bag in your trunk and you weren't being arrested for armed robbery or something like that, I highly doubt you have an issue. You might want to consider leaving the knife at home when you're not going hiking though.
I don't live in MA, ME, or NH though, so check your local laws. Some areas have zero tolerance on fixed blade knives and knives over four inches in length to the cutting edge of the blade.
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